Organic electroluminescent devices (OED) are generally composed of single or multiple layers of organic materials sandwiched between transparent and metallic electrodes. OEDs are attractive owing to the requirement for low driving voltage and the fact that they are generally simple and relatively easy and inexpensive to fabricate even for sizes as small as a tenth of a millimeter in diameter. Furthermore, the light generated by OEDs are sufficient for use in a variety of ambient light conditions (from little or no ambient light to bright ambient light). Because of these advantages OEDs have a potential application in full color flat emissive displays as well as displays in small products, such as pagers, cellular and portable telephones, two-way radios, data banks, etc.
A major problem with OEDs is the injection barrier between the electrical contacts and the carrier transporting layers, which reduces the efficiency of the device. To avoid this problem, better band alignment between the contacts and the organic layers is needed. In the prior art, this is primarily done by using low work function metals such as Li, Ca and Mg as the cathode. These metals are highly susceptible to moisture which complicates the fabrication and encapsulation process resulting in an increase in cost. Other methods utilized to increase the device efficiency involve the use of dopants, such as N,N'-dimethylquinacridone as the primary fluorescer. Though significant improvements in the performance of OEDs have been achieved in this manner in the prior art (See U.S. Pat. No. 5,593,788), these devices still employ reactive metals as the cathode.
Accordingly, it would be beneficial to provide an OED which avoids these problems.
It is a purpose of the present invention to provide for an efficient and stable OED without the use of reactive metals and a method of fabrication.
It is another purpose of this invention to provide for a new method to enhance carrier injection into the organic electroluminescent medium of an OED without the use of reactive metals.
It is further purpose of the present invention to provide organic electroluminescent devices with enhanced charge transport.
It is a further purpose of this invention to provide for an OED with improved performance and reliability.